The specific aims of this proposal are to: (1) Characterize mos-associated proteins by multiple approaches including co-fractionation with epitope-tagged mos, coprecipitation with mos, binding assays with mos immobilized on nitrocellulose paper. (2) Identify mos-interacting proteins by using improved yeast two-hybrid system. (3) Identify p35CdK, which associates with v-mos in MSV transformed NIH3T3 cells, and determine the physiological significance of this interaction. (4) Analyze the mechanism of activation of MAP kinase (MEK 1 and 2) in v-mos transformed cells. (5) Determine the relationship of v-mos to a signal transduction pathway involving ras and raf-1 by identification of additional v-mos substrates. (6) Study the effect of v-mos kinase on the activity of various CdKS.